Conventional transportation fuels (e.g., gasoline, diesel, jet fuel, etc.) are typically derived from non-renewable raw materials such as petroleum. However, the production, transportation, refining and separation of petroleum to provide transportation fuels is problematic in a number of significant ways.
For example, petroleum (e.g., crude oil and/or natural gas) production poses a number of environmental concerns. First, the history of petroleum production includes many incidents where there have been uncontrolled releases of crude petroleum during exploration and production (e.g., drilling) operations. While many of these incidents have been relatively minor in scale, there have been a number of incidents that have been significant in scale and environmental impact (e.g., BP's Deepwater Horizon incident, Mississippi Canyon, Gulf of Mexico, 2010).
In addition, world petroleum supplies are finite. Thus, as world petroleum demand has increased (84,337 M bpd worldwide in 2009; US Energy Information Administration), easily accessible reserves have been depleted. Accordingly, petroleum exploration and production operations are more frequently conducted in remote and/or environmentally sensitive areas (e.g., deepwater offshore, arctic regions, wetlands, wildlife preserves, etc.). Some remote locations require highly complex, technically challenging solutions to locate and produce petroleum reserves (e.g., due to low temperatures, water depth, etc.). Accordingly, the potential for large-scale environmental damage resulting from uncontrolled discharge of petroleum during such complex, technically challenging exploration and production operations is substantively increased.
Furthermore, when petroleum is produced in remote areas and/or areas which do not have infrastructure (e.g., refineries) to further process petroleum into useful products, the produced petroleum must be transported (e.g., via pipeline, rail, barge, ship, etc.), often over significant distances, to terminal points where the petroleum products may be refined and/or processed. Transportation of petroleum is also an operation with associated risk of accidental discharge of petroleum in the environment, with concomitant environmental damage, and there have been a number of significant incidents (e.g., Exxon's Valdez tanker spill, Prince William Sound, Ak., 1989). Furthermore, much of the world's proven petroleum reserves are located in regions which are politically unstable. Accordingly, supplies of petroleum from such regions may be uncertain since production of petroleum or transportation of petroleum products from such regions may be interrupted.
Petroleum is a complex mixture of chemical compounds. Crude petroleum comprises chemical entities from very the simple, e.g., helium and methane prevalent in natural gas, to the complex, e.g., asphaltenes and heterocyclic organic compounds prevalent in heavy, sour crude oil. Furthermore, crude petroleum is typically co-produced with varying amounts of formation water (e.g., water from the rock formation from which the petroleum was produced), often as stable emulsion, with salts, metals and other water-soluble compounds dissolved in the formation water. Crude oil may also contain varying amounts of particulate salts, metals, sediments, etc. Accordingly, crude oil streams are typically desalted, then allowed to settle and phase-separate into crude and water fractions, reducing the water content of the crude and the level of undesired components such as salts, metals, silt, sediment, etc. which may be present in the crude. Such undesired components are generally problematic in further processing and/or refining of petroleum into commercially useful fractions. For example, certain unit operations in the refining process may be sensitive to water, salt or sediment. Further, piping, storage and process vessels employed in the transport, storage and processing of petroleum is prone to corrosion, which may be accelerated and/or exacerbated by the presence of salt and/or water in the petroleum feedstock.
Desalting processes typically require the use of large quantities of water, which also may be heated, to extract salt and soluble metals from the crude oil. Further, the crude stream to be desalted is also generally heated to effect mixing with the extraction water. The resulting emulsions may then be treated with demulsifying agent and allowed to settle prior to further processing. Such desalting (and settling) may be time consuming, and may require (i) large quantities of water to extract the undesirable components, (ii) large amounts of energy to heat the water and/or crude stream(s) to effect mixing, and (iii) the use of substantial quantities of chemical agents to treat the crude (e.g., demulsifiers). As a result, large quantities of contaminated water are produced in desalting operation which must be treated to remove residual oil, dissolved salts, metals, water-soluble organics, demulsifiers, etc.
Furthermore, crude petroleum from various regions, different subterranean reservoirs within a region, or even from different strata within a single field may have different chemical compositions. For example, crude oils can range from “light, sweet” oils which generally flow easily, and have a higher content of lower molecular weight hydrocarbons and low amounts of contaminants such as sulfur, to heavy, sour oils, which may contain a large fraction of high molecular weight hydrocarbons, large amounts of salts, sulfur, metals and/or other contaminants, and may be very viscous and require heating to flow. Furthermore, the relative amounts of the constituent fractions (e.g., light, low molecular weight hydrocarbons vs. heavier, higher molecular weight hydrocarbons) of the various grades or types of crude oil varies considerably. Thus, the chemical composition of the feedstock for a refinery may vary significantly, and as a result, the relative amounts of the hydrocarbon streams produced may vary as a function of the crude feed.
Once the crude feedstock is sufficiently treated to remove undesired impurities or contaminants, it can then be subject to further processing and/or refining. The crude feedstock is typically subject to an initial distillation, wherein the various fractions of the crude are separated into distillate fractions based on boiling point ranges. This is a particularly energy intensive process, as this separation is typically conducted on a vast scale, and most or all of the feedstock is typically heated in the distillation unit(s) to produce various distillate fractions. Furthermore, since the crude composition is quite complex, containing hundreds of compounds (if not more), each fraction may contain many different compounds, and the composition and yield of each distillate fraction may vary depending on the type and composition of crude feedstock. Depending on the desired product distribution on the back end of a refining operation, a number of additional refining steps may be performed to further refine and/or separate the distillate streams, each of which may require additional equipment and energy input.
For example, higher boiling fractions from an initial distillation may be subject to further distillation (e.g., under vacuum) to separate the mixture even further. Alternatively, heavy fractions from an initial distillation may be subject to “cracking” (e.g., catalytic cracking) at high temperatures to reduce the average molecular weight of the components of the feed stream. Since lighter hydrocarbon fractions (e.g., containing less than 20 carbon atoms) generally have greater commercial value and utility than heavier fractions (e.g., those containing more than 20 carbon atoms), cracking may be performed to increase the value and/or utility of a heavy stream from an initial distillation. However, such cracking operations are typically very energy intensive since high temperatures (e.g., 500° C.) are generally required to effect the breakdown of higher molecular weight hydrocarbons into lower molecular weight components. Furthermore, the output from such cracking operations is also a complex mixture, and accordingly, may require additional separation (e.g., distillation) to separate the output stream into useful and/or desired fractions having target specifications, e.g., based on boiling point range or chemical composition.
Accordingly, the various component streams produced from petroleum refining and/or processing are generally mixtures. The homogeneity or heterogeneity of those mixtures may be a factor of the character of the crude feedstock, the conditions at which separations are conducted, the characteristics of a cracked stream, and the specifications of an end user for purity of a product stream. However, in practical terms, higher purity streams will require more rigorous separation conditions to isolate a desired compound from related compounds with similar boiling points (e.g., compounds having boiling points within 20, 10, or 5° C. of each other). Such rigorous separations generally require large process units (e.g., larger distillation columns) to separate more closely related compounds (e.g., compounds which have relatively close boiling points).
Furthermore, in addition to the above-described environmental concerns and energy/infrastructure costs associated with petroleum production and refining, there is mounting concern that the use of petroleum as a basic raw material in the production of fuels contributes to environmental degradation (e.g., global warming) via generation and/or release of oxides of carbon. For example, burning a gallon of typical gasoline produces over 19 pounds of carbon dioxide. Because no carbon dioxide is consumed by a refinery in the manufacture of gasoline, the net carbon dioxide produced from burning a gallon of petroleum-derived gasoline is at least as great as the amount of carbon contained in the fuel, and is typically higher when the combustion of additional petroleum required to power the refinery (e.g., for separation of petroleum to produce the gasoline) and to power the transportation vehicles, pumps along pipelines, ships, etc. that bring the fuel to market is considered.
In contrast to fossil fuels, the net carbon dioxide produced by burning a gallon of biofuel or biofuel blend, or by producing biomass derived chemicals is less than the net carbon dioxide produced by burning a gallon of petroleum derived fuel or in producing chemicals from petroleum. In addition, biomass-derived chemical and fuel production has far fewer environmental hazards associated with it, since production of biomass-derived fuels requires no drilling operations. Further, biomass-derived chemical and fuel facilities can be located in a wide range of locations relative to petroleum refineries, essentially almost anywhere appropriate feedstocks are available (e.g., where sufficient amounts of suitable plant matter are available). Thus, the requirement for transport of feedstock can minimized, as are the associated energy costs of such transport. Further, even if transport of raw materials is needed, the environmental hazards of a spill of a typical biomass feedstock (e.g., corn) are negligible. Furthermore, biomass-derived product streams are typically far less complex mixtures than product streams from petroleum refining operations. Thus, far less energy may be required to obtain product streams having desired molecular weight distributions and/or purity characteristics from biomass-based chemical production operations.
Biofuels have a long history ranging back to the beginning on the 20th century. As early as 1900, Rudolf Diesel demonstrated an engine running on peanut oil. Soon thereafter, Henry Ford demonstrated his Model T running on ethanol derived from corn. However, petroleum-derived fuels displaced biofuels in the 1930s and 1940s due to increased supply and efficiency at a lower cost.
At present, biofuels tend to be produced using local agricultural resources in many relatively small facilities, and are viewed as providing a stable and secure supply of fuels independent of the geopolitical problems associated with petroleum. At the same time, biofuels can enhance the agricultural sector of national economies. In addition, environmental concerns relating to the possibility of carbon dioxide related climate change is an important social and ethical driving force which is triggering new government regulations and policies such as caps on carbon dioxide emissions from automobiles, taxes on carbon dioxide emissions, and tax incentives for the use of biofuels.
The acceptance of biofuels depends primarily on their economic competitiveness compared to petroleum-derived fuels. As long as biofuels are more expensive than petroleum-derived fuels, the use of biofuels will be limited to specialty applications and niche markets. Today, the primary biofuels are ethanol and biodiesel. Ethanol is typically made by the fermentation of corn in the US and from sugar cane in Brazil. Ethanol from corn or sugar cane is competitive with petroleum-derived gasoline (exclusive of subsidies or tax benefits) when crude oil stays above $50 per barrel and $40 per barrel, respectively. Biodiesel is competitive with petroleum-based diesel when the price of crude oil is $60/barrel or more.
In addition to cost, the acceptance of biofuels is predicated on their performance characteristics, their ability to run in many types of existing equipment, and their ability to meet demanding industry specifications that have evolved over the last century. Fuel ethanol has achieved only limited market penetration in the automotive market in part due to its much lower energy content compared to gasoline, and other properties (such as water absorption) that hinder its adoption as a pure fuel. To date, the maximum percentage of ethanol used in gasoline has been 85% (the E85 grade), and this has found use in only a small fraction of newer, dual-fuel cars where the engines have been redesigned to accommodate the E85 fuel.
Acceptance of biofuels in the diesel industry and aviation industry has lagged even farther behind that of the automotive industry. Methyl trans-esterified fatty acids from seed oils (such as soybean, corn, etc.) have several specific disadvantages compared to petroleum-derived diesel fuels, particularly the fact that insufficient amounts of seed oil are available. Even under the most optimistic scenarios, seed oils could account for no more than 5% of the overall diesel demand. Furthermore, for diesel and aviation engines, the cold flow properties of the long chain fatty esters from seed oils are sufficiently poor so as to cause serious operational problems even when used at levels as low as 5%. Under cold conditions, the precipitation and crystallization of fatty paraffin waxes can cause debilitating flow and filter plugging problems. For aviation engines, the high temperature instability of the esters and olefinic bonds in seed oils is also a potential problem. To use fatty acid esters for jet fuel, the esters must be hydrotreated to remove all oxygen and olefinic bonds. Additionally, jet fuels must contain aromatics in order to meet the stringent energy density and seal swelling demands of jet turbine engines. Accordingly, synthetic jet fuels including hydrotreated fatty acid esters from seed oils, or synthetic fuels produced from coal must be blended with aromatic compounds derived from fossil fuels to fully meet jet fuel specifications.
Accordingly, there is a need for improved renewable jet fuel blendstocks and jet fuel blends with costs and performance properties comparable to, or superior to existing jet fuels, and which meet or exceed the requirements of ASTM D7566 10a for aviation turbine fuel containing synthetic hydrocarbons.